Late swerve - the phenomenon

So last season's project to webcast from the alley drew to an unsatisfactory conclusion, limited by funds rather than technology - wife saw vodafone bill!

This season my chosen topic is late swerve, defined as the ability (or uncontrollable tendency) to make the ball swerve within the last third of the alley as it approaches the skittles. We all know that it happens occasionally and, all other things being equal, we know that it can dramatically increase the chances of hitting wood. So what causes it?

Let's start with a visit to The Geordies website where analysis is presented for the swerve of a perfectly spherical, homogeneous spinning ball on a perfectly plane horizontal alley. The conclusion is that any swerve should be exhibited within the first third of the ball's travel down the alley; thereafter the trajectory should be straight. This finding was investigated by nuclear ballistics expert Dr John Harbottle and Head Coach Jeff Price in experiments under carefully controlled conditions on The Geordies home alley at Thornbury Rugby Club on 4 December 2006. Most of the time the swerve due to spin was exhibited only within the first third of the alley. Yet late swerve occurred occasionally!

So we conclude that the phenomenon exists and must be a manifestation of some feature(s) of a real ball on a real surface.

The tests completed by Harbottle and Price showed that delivery of The Geordies' balls without spin resulted in no swerve, neither early nor late. We conclude that the Thornbury Rugby Club alley is a good approximation to the ideal - plane and horizontal. My future theoretical exploration must therefore probe the impact on dynamics caused by the departure of our balls from the ideal.